1. Field of the Invention
The present invention relates to a display device and an electronic device including the display device.
2. Description of the Related Art
With the widespread use of large display devices such as liquid crystal televisions, display devices are required to be higher-value-added and thus are under development. Particularly, a technique to form a driver circuit or part of a driver circuit over a substrate, where a pixel portion is formed, using thin film transistors (TFTs) whose channel region is formed using an amorphous semiconductor or a microcrystalline semiconductor is actively developed because the technique greatly helps a reduction in cost and improvement in reliability.
Instead of forming a signal line driver circuit (a source driver) over a substrate where a pixel portion is formed, in a display device using transistors whose channel regions are formed using an amorphous semiconductor or a microcrystalline semiconductor, by using a technique called COG (chip on glass) or COF (chip on film), a video signal is input from a driving IC through connection terminals which are provided as many as signal lines. The number of the connection terminals which are provided as many as the signal lines is increased as the number of the signal lines is increased, which causes a rise of cost. Patent Document 1 discloses a structure in which three analog switches are provided for signal lines in a signal line driver circuit and are provided over the same substrate as a pixel portion and one horizontal scanning period has three writing periods.
In recent years, display devices in which light emitting elements such as EL elements are driven (EL display devices) have been actively developed. Patent Document 2 discloses a structure of a pixel circuit in which the number of transistors provided in a pixel is reduced and variations in threshold voltage and field-effect mobility between the transistors can be compensated.